Lignin-based liquid metal photo-thermal composite material as well as preparation method and application thereof

Abstract

The invention discloses a lignin-based liquid metal photo-thermal composite material, a preparation method and application of the lignin-based liquid metal photo-thermal composite material in the fields of solar seawater desalination and industrial wastewater purification, and belongs to the technical field of new energy materials. The preparation method of the lignin-based liquid metal photo-thermal composite material comprises the following steps of lignin pretreatment, acidification process, separation and post-treatment and mechanochemical synthesis. A planetary mixer is adopted, phenolic hydroxyl groups of lignin and an oxide layer on the surface of liquid metal generate coordination, the stable and adhesive photo-thermal composite material is formed, and the potential of wide application of the photo-thermal composite material in different fields is remarkably enhanced; more importantly, the preparation method provided by the invention is green and efficient, overcomes the defects of tedious steps and complex chemical reactions when the functionalized lignin-based photo-thermal material is prepared in the prior art, and can improve the sunlight absorption performance and photo-thermal conversion capability of the photo-thermal composite material by virtue of the interaction force between the lignin and the liquid metal.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials, and specifically relates to a lignin-based liquid metal photothermal composite material, a preparation method and its application in the fields of solar seawater desalination and industrial wastewater purification. Background Art

[0002] The present invention provides a simple method for preparing a lignin-liquid metal photothermal composite material based on mechanochemistry, belonging to the field of photothermal materials technology. The invention utilizes a planetary mixer to provide mechanical and shear forces, then utilizes the wettability of liquid metal to mix with lignin in an air system to prepare the lignin-liquid metal composite material. During the composite process, the hydroxyl groups of the lignin bond with the liquid metal surface through hydrogen bonds and coordination bonds, reducing the composite material's optical band gap, improving its light absorption capacity, and enhancing its solar thermal conversion capability. Leveraging the composite material's adhesive properties, a wood evaporator coated on a delignified balsa wood surface achieves excellent seawater desalination performance. Summary of the Invention

[0003] In response to the problems existing in the prior art, the present invention aims to provide a lignin-based liquid metal photothermal composite material, a preparation method and its application. The lignin-based liquid metal photothermal composite material prepared by utilizing the phenolic hydroxyl groups on the surface of the lignin base to coordinate with the liquid metal photothermal has excellent ultraviolet absorption performance, photothermal conversion performance and salt resistance. It can perform solar evaporation in seawater and high-concentration salt water to produce clean fresh water, providing a green, environmentally friendly, efficient and stable photothermal conversion material for solar seawater desalination.

[0004] The specific technical solutions are as follows: A method for preparing a lignin-based liquid metal photothermal composite material, comprising the following steps: S1 Lignin pretreatment: Add lignin and sodium hydroxide solution to a round-bottom flask, stir at 400-500 rpm, and react at 23-27°C for 24 hours. Then, vacuum filter and collect the filtrate to obtain a clarified filtrate for later use. The concentration of the sodium hydroxide solution is 1-3 mol / L, and the mass ratio of lignin to sodium hydroxide is 1:3-6. S2 Acid precipitation process: The obtained clarified filtrate is transferred to a jacketed reactor with temperature control. The circulating water bath is adjusted to stabilize the system temperature at 65-75 °C. At a stirring speed of 300-500 rpm, 50 wt%-70 wt% sulfuric acid is added dropwise. The pH change is monitored in real time. When the system pH reaches 1.9-2.0, the acid addition is immediately stopped. Stirring is continued for 10-20 min until the particles are matured to obtain a solid-liquid mixture after acid precipitation. S3 separation and post-treatment: The solid-liquid mixture obtained after acid precipitation is rapidly hot filtered using a preheated Buchner funnel, and hot washed three times with deionized water at 65-75°C. After each washing, the mixture is centrifuged and dried until the pH value of the filtrate is neutral, and the filter residue is collected; the Buchner funnel is preheated to 60-70°C; the centrifugal speed is 3000-5000 rpm, and the centrifugation time is 10-20 min to obtain purified lignin; S4 mechanochemical synthesis: the obtained filter residue and liquid metal are mixed and placed in a polypropylene plastic tank, and the mixture is placed in a planetary mixer for reaction to obtain a lignin-liquid metal photothermal composite material.

[0005] In some embodiments, the lignin is a combination of one or more of dealkalized lignin, alkaline lignin, sodium lignin sulfonate, and calcium lignin sulfonate.

[0006] In some embodiments, the liquid metal is a gallium-indium alloy, a gallium-indium-tin alloy, or a combination thereof.

[0007] In some embodiments, the mass ratio of the purified lignin to the liquid metal in S4 is 1-10:1.

[0008] In some embodiments, the reaction conditions of the planetary mixer are a rotation speed of 2000-2500 rpm and a time of 20-60 min.

[0009] The present invention also provides a lignin-liquid metal photothermal composite material prepared by the above preparation method.

[0010] The lignin-liquid metal photothermal composite material prepared by the present invention has applications in the fields of solar seawater desalination and industrial wastewater purification.

[0011] The lignin-liquid metal photothermal composite material prepared by the present invention is used in the fields of solar seawater desalination and industrial wastewater purification. The method of use is as follows: delignified balsa wood is treated with a plasma cleaner for 5 to 10 minutes, and the obtained lignin-liquid metal photothermal composite material is coated on the surface of the delignified balsa wood to obtain a wood photothermal evaporator. The obtained wood photothermal evaporator is floated on the surface of seawater or industrial wastewater, and seawater desalination and wastewater purification can be achieved under sunlight to obtain pure fresh water.

[0012] The present invention has the following advantages: (1) The present invention uses a planetary mixer to synthesize a lignin-liquid metal photothermal composite material with excellent solar thermal conversion performance. During the synthesis process, the phenolic hydroxyl groups of the lignin coordinate with the oxide layer on the surface of the liquid metal to form a stable photothermal composite material; (2) The photothermal composite material prepared by the present invention has adhesive properties, which significantly enhances its potential for wider application in different fields; (3) The method of the present invention is green and efficient, overcoming the tedious steps and complex chemical reactions used in the prior art to prepare functionalized lignin-based photothermal materials. By leveraging the interaction between lignin and liquid metal, the solar absorption performance and photothermal conversion capacity of the photothermal composite material can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the process of preparing the lignin-liquid metal photothermal composite material according to Example 1 of the present invention; Figure 2 This is a molecular schematic diagram of the lignin-liquid metal photothermal composite material prepared in Example 1 of the present invention; Figure 3 This is a physical picture of the lignin-liquid metal photothermal composite material prepared in Example 1 of the present invention; Figure 4 This is a SEM image of the lignin-liquid metal photothermal composite material prepared in Example 1 of the present invention; Figure 5 The photothermal conversion effect of the lignin-liquid metal photothermal composite material prepared in Example 1 of the present invention under simulated sunlight; Figure 6 This is the UV-visible light absorption graph of the lignin-liquid metal photothermal composite material prepared in Example 1 of the present invention; Figure 7 This is a photothermal curve diagram of the lignin-liquid metal photothermal composite material prepared in Example 1 of the present invention at different power densities; Figure 8 The evaporation rate performance of the wooden photothermal evaporator prepared in Example 3 of the present invention in brine of different concentrations; Figure 9 This is a curve showing the change in ion concentration of seawater before and after evaporation by the wood photothermal evaporator prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings, technical process steps, specific implementation conditions and materials in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Example 1

[0016] like Figure 1As shown, 20g of dealkalized lignin raw material was weighed and added to 80g of 2 mol / L sodium hydroxide solution. The mixture was stirred at 500 rpm for 24 hours to promote dissolution. The temperature was controlled at 25°C. It was then heated to 70°C, and 60 wt% sulfuric acid was added to adjust the pH to 2. The pretreated lignin was filtered and dried while hot. 5g of pretreated dealkalized lignin was weighed and mixed with 1g of liquid metal (75wt% gallium Ga, 25 wt% indium) and placed in a polypropylene plastic jar. The mixture was placed in a planetary mixer for reaction. The reaction conditions were set at a speed of 2200 rpm and a time of 30 minutes. The molecular schematic diagram of the reaction is shown below. Figure 2 As shown, after the reaction is completed, the residual liquid metal is removed, and the resulting solid powder is the lignin-liquid metal photothermal composite material. The optical photograph is shown in Figure 3 Scanning electron microscopy analysis was performed, and the results Figure 4 As shown, the prepared lignin-liquid metal photothermal composite material presents a core-shell structure.

[0017] Example 2

[0018] The prepared lignin-liquid metal photothermal composite material was irradiated under simulated sunlight, and an infrared thermal imager was used to monitor the real-time temperature and detect the temperature change of the coating surface, such as Figure 5 As shown in the figure, the peak temperature is about 53 °C, indicating that the lignin-liquid metal photothermal composite material has excellent photothermal conversion ability. The temperature rise curve of the prepared lignin-liquid metal photothermal composite material under different solar power was further tested, as shown in the figure. Figure 6 As shown in the figure, its equilibrium temperature increases with the increase of the power density of the solar simulator, indicating that the maximum equilibrium temperature of the composite material can be flexibly adjusted by adjusting the power density of the solar simulator, and at the same time, the excellent light responsiveness of the composite material is demonstrated. An appropriate amount of lignin-liquid metal photothermal composite material was weighed and the light absorption performance was measured using a UV-visible spectrometer with an integrating sphere. 100 mg of lignin-liquid metal photothermal composite material was weighed and the light absorption spectrum was tested. The results are shown in the figure. Figure 7 As shown, the lignin-liquid metal photothermal composite material exhibits strong light absorption ability in the ultraviolet and visible light bands. It can be seen that the prepared lignin-liquid metal photothermal composite material has excellent light absorption performance.

[0019] Example 3

[0020] After the delignified balsa wood was treated with a plasma cleaner for 5 minutes, the lignin-liquid metal photothermal composite material prepared in Example 1 was coated on the surface of the delignified balsa wood at a coating amount of 100 g / m 2 , and obtain a wood photothermal evaporator. The obtained wood photothermal evaporator was used to carry out evaporation experiments on salt water with different concentrations. The results are as follows Figure 8As shown in Figure 2, the water evaporation rate gradually decreases with the increase of brine concentration. However, it is worth mentioning that even in brine with a concentration of 20 wt%, the water evaporation rate is still 1.73 kg m -2 h -1 , indicating that the wooden photothermal evaporator has excellent salt tolerance and can operate efficiently in high-concentration salt water, showing great application potential in the field of solar desalination. The photothermal conversion efficiency of the prepared wooden photothermal evaporator is 95.94%. The evaporation rate and evaporation efficiency are calculated according to the following formula: ; Where V is the evaporation rate, Δm is the change in mass of water, Δt is the time, and s is the surface area of the photothermal layer.

[0021] Where, is the enthalpy of vaporization of water, is the net mass change rate of water, is the solar absorption rate of the evaporator, is the power of incident simulated sunlight.

[0022] Example 4

[0023] The wooden photothermal evaporator prepared in Example 3 was placed in real seawater for evaporation experiments. The water vapor generated by evaporation was condensed into liquid water, which was collected and recorded as evaporated seawater. Four representative ions in seawater, namely K + , Ca 2+ 、Na + and Mg 2+ The concentration changes before and after evaporation are as follows Figure 9 As shown, K + , Ca 2+ 、Na + and Mg 2+ The concentration of water decreased by two to three orders of magnitude after evaporation and met the drinking water quality guidelines set by the World Health Organization, indicating that the wood-based thermal evaporator has excellent seawater desalination performance.

[0024] Technical personnel should note: Although the present invention has been described according to the above specific implementation methods, the inventive concept of the present invention is not limited to this invention. Any modification using the inventive concept will be included in the scope of protection of this patent.

Claims

1. A method for preparing a lignin-based liquid metal photothermal composite material, characterized in that: The preparation method of the lignin-based liquid metal photothermal composite material comprises the following steps: S1 Lignin pretreatment: Add lignin and sodium hydroxide solution to a round-bottom flask, stir at 400-500 rpm, and react at 23-27°C for 24 hours. Then, vacuum filter and collect the filtrate to obtain a clarified filtrate for later use. The concentration of the sodium hydroxide solution is 1-3 mol / L, and the mass ratio of lignin to sodium hydroxide is 1:3-6. S2 Acid precipitation process: The obtained clarified filtrate is transferred to a jacketed reactor with temperature control. The circulating water bath is adjusted to stabilize the system temperature at 65-75 °C. At a stirring speed of 300-500 rpm, 50 wt%-70 wt% sulfuric acid is added dropwise. The pH change is monitored in real time. When the system pH reaches 1.9-2.0, the acid addition is immediately stopped. Stirring is continued for 10-20 min until the particles are matured to obtain a solid-liquid mixture after acid precipitation. S3 separation and post-treatment: The solid-liquid mixture obtained after acid precipitation is rapidly hot filtered using a preheated Buchner funnel, and hot washed three times with deionized water at 65-75°C. After each washing, the mixture is centrifuged and dried until the pH value of the filtrate is neutral, and the filter residue is taken; the Buchner funnel is preheated to 60-70°C; the centrifugal speed is 3000-5000 rpm, and the centrifugation time is 10-20 min to obtain purified lignin; S4 mechanochemical synthesis: the obtained filter residue and liquid metal are mixed and placed in a polypropylene plastic tank, and the mixture is placed in a planetary mixer for reaction to obtain a lignin-liquid metal photothermal composite material.

2. The method for preparing a lignin-based liquid metal photothermal composite material according to claim 1, characterized in that: The lignin is a combination of one or more of dealkalized lignin, alkaline lignin, sodium lignin sulfonate, and calcium lignin sulfonate.

3. The method for preparing a lignin-based liquid metal photothermal composite material according to claim 1, characterized in that: The liquid metal is a gallium-indium alloy, a gallium-indium-tin alloy, or a combination thereof.

4. The method for preparing a lignin-based liquid metal photothermal composite material according to claim 1, characterized in that: The mass ratio of the purified lignin to the liquid metal in S4 is 1-10:

1.

5. The preparation method according to claim 1, characterized in that The reaction conditions of the planetary mixer are a rotation speed of 2000-2500 rpm and a reaction time of 20-60 min.

6. A lignin-liquid metal photothermal composite material prepared according to the method for preparing a lignin-based liquid metal photothermal composite material according to any one of claims 1 to 5.

7. Application of the lignin-liquid metal photothermal composite material prepared by the method for preparing a lignin-based liquid metal photothermal composite material according to any one of claims 1 to 5 in the fields of solar seawater desalination and industrial wastewater purification.

8. The application of a lignin-based liquid metal photothermal composite material in the field of solar seawater desalination and industrial wastewater purification according to claim 7, characterized in that: The method of use is: after treating delignified balsa wood with a plasma cleaning machine for 5 to 10 minutes, the obtained lignin-liquid metal photothermal composite material is coated on the surface of the delignified balsa wood to obtain a wood photothermal evaporator, and the obtained wood photothermal evaporator is floated on the surface of seawater or industrial wastewater. Seawater desalination and sewage purification can be achieved under sunlight to obtain pure fresh water.

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